1. Field of the Invention
The present invention relates to a process for manufacturing catalysts for heterogeneous synthesis, particularly for ammonia, in which a mixture of magnetite and promoters, especially oxides of calcium, magnesium aluminium, potassium and silicon is prepared, the so obtained mix is molten at least at 1600.degree. C., the molten mass is air cooled, freed from slag, crushed, milled in a rod-mill and possibly added with a binder and water, the powders are pelletised in a tray pelletiser, dried at 100.degree. C. to 150.degree. C. and sintered at 1200.degree. to 1350.degree. C. in argon atmosphere.
2. Description of the Prior Art
Such a process is described in the Italian Pat. No. 1002.972 (now assigned to the Applicant), corresponding to U.S. Pat. No. 4,073,749. In such patent neither the milling degree (grinding fineness) nor the size choice of the powders are indicated: the specification lets suppose that the parameter of the powder size be without influence also in view of the fact that the powders are utilized to form granules which act as growing centres of spheres that shall have higher diameters than those of the starting granules because these last granules shall absorb powder during their pelletisation.